This invention concerns a pneumatic valve recoil system for an internal combustion engine, usable primarily--but not exclusively--for automotive purposes.
In order to ensure proper operation of the motor, a recoil system needs to be used to keep the intake and exhaust valves in the closed position, with said valves opening at the desired time by the action of cams or rocker arms actuated by a cam shaft.
The recoiling of valves is generally done by using metal helical springs, but these springs have a certain number of drawbacks, particularly the phenomenon known by the name of "valve flutter."
It is a known fact that the natural vibrational frequency of a spring drops as its deflection increases. This is how valve springs start to vibrate at relatively slow engine speeds when the valve lift has been designed to be large. The result on this type of engine is excessively low power at high engine speeds in spite of the good theoretical admission. This is why pneumatic systems have been proposed for valve recoiling.
Document FR-A-2529616 describes such a system in which the valve stem is one with a piston sliding in a cylinder, which together define a chamber filled with a compressible fluid such as air. Since the chamber cannot be perfectly sealed,l air leaks and oil infiltration still occur. For this reason an air-supply and oil-evacuation system using lines with calibrated valves is provided, in which the lines are made in the bodies of the pneumatic springs which are in turn installed in the engine's cylinder head.
This system, however, is complex to make because many passages have to be drilled, and it requires delicate adjustment since a large number of springs need to be installed and calibrated.